Immediate post-training ICV administration of a synthetic peptide homologous to .beta.-A4, [Gln.sup.11 ].beta.-(1-28) Asp Ala Glu Phe Arg His Asp Ser Gly Tyr Gln Val His Gln Lys Leu Val Phe Phe Ala Glu Asp Val Gly Ser Asn Lys (SEQ ID NO: 1)] caused amnesia for FAAT in mice in dose-dependent fashion. Also amnestic were residues .beta.-(12-28) [Val His His Gln Lys Leu Val Phe Phe Ala Glu Asp Val Gly Ser Asn Lys (SEQ ID NO: 2)], .beta.-(18-28) [Val Phe Phe Ala Glu Asp Val Gly Ser Asn Lys (SEQ ID NO: 3)], and .beta.-(12-20) [Val His His Gln Lys Leu Val Phe Phe (SEQ ID NO: 4)](1). These amnestic peptides have in common the tripeptidic sequence Val Phe Phe (SEQ ID NO: 5). Residue .beta.-(1-11) [Asp Ala Glu Phe Arg His Asp Ser Gly Tyr Gln (SEQ ID NO: 6)], which does not contain Val Phe Phe, was not amnestic (this study). FAAT experiments were performed with peptides containing the Val Phe Phe sequence from which was derived a topographic model for the binding site of amnestic peptides. Since the amnestic substances are memory-enhancing at lower concentration than those at which they cause amnesia, the model can be used to deduce the structure of potential memory-enhancing peptides and non-peptidic substances.